27. Explain, with reference to examples, the meaning of the term chemical equivalent. July 1844.

Chemical equivalent is a definite weight of one element capable of replacing a definite weight of another element. Since 35.5 parts by weight of chlorine combine with one part by weight of hydrogen to form hydric chloride, 35.5 parts by weight of chlorine are said to be equivalent to 1 part by weight of hydrogen. Also, since 2 parts by weight of hydrogen combine with 16 parts by weight of oxygen to form water, 8 parts by weight of oxygen are said to be equivalent to 1 part by weight of hydrogen. So also, as 35'5 parts by weight of chlorine are equivalent to 1 part by weight of hydrogen, they are by deduction equivalent to 8 parts by weight of oxygen.

28. Explain what is meant by combining proportions, equivalents, or atomic numbers. July 1849.

The examiner takes these three expressions as synonymous. They refer to the proportions, or to the multiples of them, in which all the bodies combine among themselves. For example, the atomic weight of hydrogen is 1, that of oxygen 16, that of nitrogen 14, that of potassium 39: therefore, when these bodies form compounds among themselves, they will always do so in some simple multiples of 1, 16, 14, 39.

29. What is the composition of the following substances :—Air, water, silica, marble, ammonia, marsh gas, and black lead or plumbago? Give the names of

The term equivalent was formerly used as synonymous with 'atomic weight;' but at present the term is scarcely used, and in its present meaning it signifies the atomic weight divided by the atomicity.

the substances represented by the following formula:CO, NO, SO2, N2O3, PH3, and NHCl. Jan. 1879.

Air, a mixture chiefly of oxygen, nitrogen, and carbonic dioxide.

Water (OH), a compound of oxygen and hydrogen.

Silica (SiO2), a compound of silicon and oxygen. Marble (CaCO3), a compound of calcium, carbon, and oxygen.

Ammonia (NH3), a compound of nitrogen and hydrogen.

Marsh gas (CH), a compound of carbon and hydrogen.

Black lead or plumbago is an allotropic modification of carbon.

The name of CO is carbonic oxide, or oxide of carbon.

NO is nitric oxide (NO2).

SO2 is sulphuric dioxide, or sulphur

ous anhydride.

N2O3 is nitric trioxide, or nitrous

anhydride.

PH, is hydric phosphide, or phosphuretted hydrogen.

NH4Cl is ammonic chloride.

30. Write the names of the following compounds: -CO, CO2, N2O, N2O3, N2O5, CH4, C2H4, SO2, SO3, and H2S. Jan. 1881.

The name of CO is carbonic oxide.

CO2 is carbonic dioxide, or carbonic acid.

N2O is nitrous oxide (laughing gas).

2

N2O3 is nitric trioxide, or nitrous anhydride.

The name of N2O5 is nitric pentoxide, or nitric

.

anhydride.

CH1 is light carburetted hydrogen (methyl hydride or marsh gas).

C2H is heavy carburetted hydrogen (ethylene, or olefiant gas).

SO2 is sulphuric dioxide, or sulphurous anhydride.

SO3 is sulphuric trioxide, or sulphuric anhydride.

H2S is hydric sulphide, or sulphuretted hydrogen.

31. Calculate the molecular weights and percentage composition of the salts having the formula CaSO, + 20H2 and BaCl2 + 20H2; and give the chemical characters by which they can be identified, and the names of the salts. Jan. 1860.

CaSO4 + 20H2 is called calcic sulphate.

40 × 100

Ca 40

= 23.26

= 18.60

172

64 × 100

= 37.21

172

36 × 100

20.93

100.00

Molec. weight = 172

BaCl2 + 20H2 is called baric chloride.

In order to identify these two salts, dissolve both in water; then add to both solutions a few drops of baric chloride. A white precipitate is formed in the solution of calcic sulphate, but not in the baric chloride. Then add to the solutions a few drops of argentic nitrate. A white precipitate is formed in the solution of baric chloride, but not in that of calcic sulphate.

32. What are the proportions by weight of the constituent elements of the following compounds :-Marsh gas, olefiant gas, carbonic acid, and water? June 1869. Marsh gas (CH). The proportions are 12 of carbon and 4 of hydrogen.

Olefiant gas (C,H). Proportions, 24 of carbon and 4 of hydrogen.

Carbonic acid (CO2). Proportions, 12 of carbon and 32 of oxygen.

Water (OH). Proportions, 16 of oxygen and 2 of hydrogen.

33. Define the chemical term acid. June 1881.

Strictly speaking, an acid is a body containing hydrogen replaceable by a metal, when that metal is presented to it in the form of a hydrate; e.g. hydric sulphate (H2SO4), hydric chloride (HCl).

When the water (OH2) has been abstracted, the body often retains the name of an acid; but it is better to prefix the term anhydrous, which means without water; e.g. SO2, SO3, N2O5.

34. Define the chemical term base. June 1881.

A base is a certain compound of a metal with oxygen, as Na2O, CaO, Fe2O3; with hydroxyl (OH), as KHO, BaH2O2, Fe2H6O6; or with nitrogen, phosphorus, &c., as NH3, PH3.

35. What are the distinctive properties of the two classes, acids and alkaline oxides or bases? What is the nature of a salt? July 1846.

What is the distinction between an alkali and an acid? What is meant by the term salt? July 1860. Define the chemical term salt.

The distinctive properties of

oxides or bases are:

June 1881.

acids and alkaline

1st. The first turn blue litmus red, and the latter turn red litmus blue.

2nd. They combine together to form salts, generally with the elimination of water.

A salt may therefore be defined as an acid in which the hydrogen has been partly or wholly replaced by a metal. If the hydrogen has been only partly removed, the salt is said to be acid; if wholly, it is said to be neutral. If more base is present than is necessary to neutralise the acid, the salt is said to be basic.

36. What is meant by the expression of the neutralisation of an acid by an alkali? What is the result of such neutralisation? July 1844.

It means that the acid and the alkali have both lost their characteristic properties, that is to are without action upon litmus paper. such neutralisation is a neutral salt.

say, that they The result of

37. What class of bodies do we call oxides? Name some oxides of an acid nature and some basic oxides. June 1867.

Oxides are a class of bodies resulting from the combination of oxygen with other elements.

1 This is not always true. Some chemically neutral salts are acid, some are basic to litmus; some chemically acid salts are basic to litmus, and vice versâ.

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